ISO 1576:1988

Overview

ISO 1576:1988 is an international standard that specifies a standardized method for determining the water-soluble and water-insoluble ash content in tea. Developed by ISO/TC 34 (Agricultural food products), this procedure involves extracting the total ash from tea samples using hot water, followed by filtration, ignition, and weighing of residues to accurately quantify insoluble ash. The soluble ash content is calculated by difference. This method ensures consistent and reliable chemical analysis of tea, supporting quality control and compliance in the tea industry.

Key Topics

• Scope and Purpose: Defines the method for determining water-soluble and insoluble ash in tea samples to ensure standardized laboratory testing.
• Apparatus Required: Includes common laboratory equipment such as silica dish (50-100 ml capacity), furnace capable of 525°C ±25°C, steam bath, ashless filter paper, desiccator with effective desiccant, and precise analytical balance.
• Test Procedure:
  • Addition of distilled water to the total ash.
  • Heating to near boiling and filtering through ashless filter paper.
  • Washing and evaporating the filtrate on a steam bath.
  • Igniting residue in a furnace and weighing after cooling to determine insoluble ash.
  • Repeated ignition and weighing until consistent mass results are obtained.
• Calculation Formulas:
  • Percentage of water-insoluble ash calculated using mass of test portion, insoluble ash, and dry matter content.
  • Water-soluble ash is derived by difference from total ash.
• Repeatability & Accuracy: The difference between two simultaneous determinations must not exceed 0.2 g per 100 g of ground sample for water-insoluble ash, ensuring test reliability.
• Reporting Requirements: Test reports must detail the method used, results, any optional operating parameters, and conditions affecting results, alongside complete sample identification.

Applications

• Quality Control in Tea Production: Monitoring ash content helps verify purity and detect contaminants or foreign materials in tea leaves.
• Regulatory Compliance: Ensures products meet safety and quality parameters mandated by food safety authorities and international trade standards.
• Research and Development: Supports scientific studies on tea composition, processing effects, and ash-related properties.
• Trade and Certification: Provides a universally recognized testing method for exporters, importers, and certification bodies to assess tea quality.
• Process Optimization: Enables manufacturers to adjust processing steps for optimal product quality by understanding ash solubility characteristics.

Related Standards

• ISO 1572:1980 - Tea - Preparation of Ground Sample with Known Dry Matter Content
• ISO 1575:1987 - Tea - Determination of Total Ash
• ISO 1577:1987 - Tea - Determination of Acid-Insoluble Ash
• ISO 1578:1975 - Tea - Determination of Alkalinity of Water-Soluble Ash

These complementary standards cover sample preparation, total ash measurement, and further chemical analyses, providing a comprehensive framework for tea quality assessment.

Keywords: ISO 1576, tea analysis, water-soluble ash, water-insoluble ash, ash determination in tea, tea quality control, chemical analysis, tea standard, agricultural food products, ISO tea standards.